The present invention relates the assessment of noise in received communications signals and to the assessment of channel quality.
In 3GPP TS 25.214 V6.7.1 “Physical layer procedures (FDD)”, the UE is required to report the channel quality indicator (CQI) for HS-DSCH rate adaptation. The definition of CQI is given as follows (TS 25.214 Section 6A.2):
“Based on an unrestricted observation interval, the UE shall report the highest tabulated CQI value for which a single HS-DSCH sub frame formatted with the transport block size, number of HS-PDSCH codes and modulation corresponding to the reported or lower CQI value could be received in a 3-slot reference period ending 1 slot before the start of the first slot in which the reported CQI value is transmitted and for which the transport block error probability would not exceed 0.1.”
The CQI values are tabulated according to UE category and have been designed to correspond to 1 dB steps in the required Signal-to-Interference plus Noise Ratio (SINR) that is required to achieve the specified BLER of 10%. In static conditions such as those implied by the definition of CQI, the relationship between the SINR and the corresponding CQI value has been established as being linear (see, for example, Brouwer, et al., “Usage of link-level performance indicators for HSDPA network-level simulations in E-UMTS,” Spread Spectrum Techniques and Applications, 2004 IEEE Eighth International Symposium on, pp. 844-848).
The UE is also supplied with the power offset between the HS-DSCH channels and the CPICH (Common Pilot Channel) and thus the determination of the CQI value can be based on the CPICH SINR.
Methods for estimating the CPICH SINR based on the despread CPICH symbols are known in the art, see e.g. “CPICH Processing for SINR Estimation in W-CDMA System”, WO2005093961.